Liquid developer

ABSTRACT

A liquid developer containing a curable insulating liquid, a cationic polymerization initiator, and a toner particle containing a binder resin and carbon black, wherein the carbon black is basic, or wherein the toner particle contains a carbon black dispersing agent, and the carbon black dispersing agent has a dispersing group and an adsorptive group, and the adsorptive group is an amino group.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a liquid developer used in animage-forming apparatus that utilizes an electrophotographic system.

Description of the Related Art

Among image-forming apparatuses that utilize electrophotographicsystems, attention has been drawn in recent years to high-speed,high-image quality digital printers based on wet developing systems,which are excellent for high-speed image formation.

Wet developing systems use a liquid developer in which toner particles,which are the developer, are dispersed in a liquid, and as a resulttoner particles can be used that are finer than in the developers usedin dry developing systems. As a consequence, wet developing systems arecharacterized by the ability to form images of higher quality than indry developing systems.

Dispersions of colored resin particles in electrically insulatingliquids, e.g., a hydrocarbon organic solvent or silicone oil, arealready known as liquid developers. However, a substantial reduction inimage quality may be caused when the electrically insulating liquidremains present on the recording medium, e.g., paper or plastic film,thorough removal of the electrically insulating liquid is required.Evaporative removal of the electrically insulating liquid through theapplication of thermal energy is the method generally used for removalof the electrically insulating liquid. However, this is not necessarilydesirable from an environmental standpoint or energy-savings standpointwhen organic solvent vapor can be discharged from the machine and/orwhen large amounts of energy are required.

A method that has been proposed as a countermeasure here is to cause theelectrically insulating liquid to undergo curing through aphotopolymerization reaction. A photocurable liquid developer uses areactive functional group-bearing monomer or oligomer as theelectrically insulating liquid and also uses a dissolvedphotopolymerization initiator.

However, when carbon black is used for the colorant in a liquiddeveloper, the photopolymerization initiator can react with the acid onthe surface of the carbon black and a so-called dark polymerizationreaction—in which the electrically insulating liquid undergoes curingbut not through a photopolymerization reaction—can then occur.

Japanese Patent Application Laid-open No. 2003-57883 does contain adescription of a dark polymerization reaction induced by thephotopolymerization initiator, but does not touch on a darkpolymerization reaction caused by a reaction between thephotopolymerization initiator and carbon black colorant. Japanese PatentApplication Laid-open No. 2012-141463 also provides a similardescription of a dark polymerization reaction, but is silent on a darkpolymerization reaction caused by a reaction between thephotopolymerization initiator and carbon black colorant.

SUMMARY OF THE INVENTION

Thus, as indicated in the preceding, several inventions that considerdark polymerization reactions in liquid developers have been disclosed.However, there is no specific mention of a dark polymerization reactionthat occurs due to the photopolymerization initiator and carbon blackpresent as a colorant. This is because it is quite difficult, withoutimpairing the fixing performance of the electrically insulating liquid,to inhibit the dark polymerization reaction that occurs due to thephotopolymerization initiator and carbon black.

Considering these circumstances, an object of the present invention istherefore to provide a liquid developer that, even though it contains aphotopolymerization initiator and a toner particle that contains carbonblack, provides an inhibition of the dark polymerizationreaction-induced curing of the electrically insulating liquid and alsohas an excellent fixing performance.

The present invention relates to a liquid developer that comprises acurable insulating liquid, a cationic polymerization initiator, and atoner particle containing a binder resin and carbon black, wherein thecarbon black is basic.

The present invention also relates to a liquid developer that contains acurable insulating liquid, a cationic polymerization initiator, and atoner particle containing a binder resin and carbon black, wherein thetoner particle contains a carbon black dispersing agent, and the carbonblack dispersing agent has a dispersing group and an adsorptive group,and the adsorptive group is an amino group.

The liquid developer of the present invention, even though it contains aphotopolymerization initiator and a toner particle that contains carbonblack, can provide an inhibition of the dark polymerizationreaction-induced curing of the electrically insulating liquid and alsohas an excellent fixing performance.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments.

DESCRIPTION OF THE EMBODIMENTS

The present invention is described in detail in the following.

Unless specifically indicated otherwise, expressions such as “at leastXX and not more than YY” and “XX to YY” that show numerical value rangesrefer in the present invention to numerical value ranges that includethe lower limit and upper limit that are the end points.

The present invention is a liquid developer that contains a curableinsulating liquid, a cationic polymerization initiator, and a tonerparticle containing a binder resin and carbon black, wherein the carbonblack is basic.

In the cationic polymerization initiator-mediated curing process ofcurable insulating liquids, generally a strong acid is first produced bythe photolysis of the cationic polymerization initiator by exposure toultraviolet radiation. This strong acid initiates the cationicpolymerization of the curable insulating liquid and the curableinsulating liquid then undergoes curing. However, the darkpolymerization reaction is not produced through the action of light. Dueto this, the present inventors carried out focused investigations intohow the dark polymerization reaction is produced.

The following was identified as a result: in the dark polymerizationreaction, the ligand of the photopolymerization initiator that isnormally released under the effect of light energy, is released due tothe action, on the photopolymerization initiator present in the curableinsulating liquid, of acidic functional groups on the surface of thecarbon black, thereby initiating the cationic polymerization of thecurable insulating liquid. The present inventors therefore carried outinvestigations on inhibiting the dark polymerization reaction byfocusing on the acidic functional groups on the carbon black surface. Asa result, they found that the use of a basic carbon black is effectivefor inhibiting the dark polymerization reaction.

The materials constituting the liquid developer of the present inventionare described in detail in the following.

<Carbon Black>

The carbon black used by the present invention characteristically isbasic.

Carbon black typically has a large number of acidic functional groups onits surface. The dark polymerization reaction is produced due to theaction of these acidic functional groups on the photopolymerizationinitiator. It was therefore thought that the use of a basic carbon blackwould be effective for suppressing the dark polymerization reaction.

Here, basic indicates that the pH is greater than 7.

The following, for example, can be used as such a carbon black: #4000B,#850, and MCF88 from Mitsubishi Chemical Corporation; Printex L andPrintex 90 from Orion Engineered Carbons; and Nipex 35 from Degussa.

The pH of carbon black can be determined according to JIS K 6221-1982.

Moreover, viewed from the standpoint of stability, the carbon blackpreferably has functional groups obtained by substitution, by alkalimetal, of a hydrogen atom in the acidic groups that are surfacefunctional groups. The reason for this is thought to be that the alkalimetal-substituted functional groups will likely reside on the carbonblack surface in a stable manner on a long-term basis.

—COOH is an example of an acidic functional group on the carbon blacksurface. The alkali metal is preferably Na or K. —COONa and —COOK arepreferred for the alkali metal-substituted functional group.

In addition, the specific surface area (BET) of the carbon black ispreferably not more than 200 m²/g, more preferably not more than 150m²/g, and still more preferably not more than 100 m²/g. This range iseffective for inhibiting the dark polymerization reaction because itprovides a smaller carbon black surface on which acid functional groupsare present and thus provides a smaller chance for contact with thephotopolymerization initiator. There are no particular limitations onthe lower limit for the specific surface area (BET) of the carbon black.The specific surface area (BET) of the carbon black can be controlledusing the particle size and surface treatments.

The carbon black can be produced by known methods and there are noparticular limitations on its method of production. Examples in thisregard are channel methods and furnace methods.

<Cationic Polymerization Initiator>

A characteristic feature of the liquid developer of the presentinvention is that it contains a cationic polymerization initiator as thephotopolymerization initiator. Cationic polymerization initiators havefast reaction rates and can provide an excellent fixing performance.

The cationic polymerization initiator preferably contains a compoundrepresented by the following formula (1).

[In formula (1), R₁ and R₂ are bonded to each other to form a cyclicstructure; x represents an integer of at least 1 and not more than 8;and y represents an integer of at least 3 and not more than 17.]

The cationic polymerization initiator represented by formula (1)undergoes photolysis upon exposure to ultraviolet radiation with theproduction of a sulfonic acid, a strong acid.

The use of the cationic polymerization initiator with formula (1), whilemaking possible an excellent fixing performance, also provides ahigh-resistance liquid developer—unlike the case for the use of an ionicphotoacid generator.

The ring structure formed by the bonding of R₁ to R₂ can be exemplifiedby five-membered rings and six-membered rings. Specific examples of thering structure formed by the bonding of R₁ to R₂ are, for example, thesuccinimide structure, phthalimide structure, norbornenedicarboximidestructure, naphthalenedicarboximide structure, cyclohexanedicarboximidestructure, and epoxycyclohexenedicarboximide structure.

These ring structures may also have, as a substituent, an alkyl grouphaving 1 to 18 carbons, an alkyloxy group having 1 to 18 carbons, analkylthio group having 1 to 18 carbons, an aryl group having 1 to 14carbons, an aryloxy group having 1 to 14 carbons, or an arylthio grouphaving 1 to 14 carbons. Another ring structure, e.g., a possiblysubstituted alicycle, heterocycle, aromatic ring, and so forth, may alsobe condensed.

The C_(x)F_(y) group, which has a strong electron-withdrawing character,is a fluorocarbon group and is a functional group for bringing aboutdecomposition of the sulfonate ester moiety upon exposure to ultravioletradiation. The number of carbon atoms here is at least 1 and not morethan 8 (x is at least 1 and not more than 8), and the number of fluorineatoms is at least 3 and not more than 17 (y is at least 3 and not morethan 17).

Synthesis of the strong acid proceeds readily when the number of carbonatoms is at least 1, while the storage stability is excellent when thenumber of carbon atoms is not more than 8. The number of carbon atoms ispreferably at least 1 and not more than 4.

Function as a strong acid is possible when the number of fluorine atomsis at least 3, while synthesis of the strong proceeds readily when thenumber of fluorine atoms is not more than 17. The number of fluorineatoms is preferably at least 3 and not more than 9.

The C_(x)F_(y) group in formula (1) can be exemplified by linear alkylgroups in which the hydrogen atom has been substituted by the fluorineatom, branched-chain alkyl groups in which the hydrogen atom has beensubstituted by the fluorine atom, cycloalkyl groups in which thehydrogen atom has been substituted by the fluorine atom, and aryl groupsin which the hydrogen atom has been substituted by the fluorine atom.

The linear alkyl groups in which the hydrogen atom has been substitutedby the fluorine atom can be exemplified by the trifluoromethyl group(x=1, y=3), pentafluoroethyl group (x=2, y=5), heptafluoro-n-propylgroup (x=3, y=7), nonafluoro-n-butyl group (x=4, y=9), perfluoro-n-hexylgroup (x=6, y=13), and perfluoro-n-octyl group (x=8, y=17).

The branched-chain alkyl groups in which the hydrogen atom has beensubstituted by the fluorine atom can be exemplified by theperfluoroisopropyl group (x=3, y=7), perfluoro-tert-butyl group (x=4,y=9), and perfluoro-2-ethylhexyl group (x=8, y=17).

The cycloalkyl groups in which the hydrogen atom has been substituted bythe fluorine atom can be exemplified by the perfluorocyclobutyl group(x=4, y=7), perfluorocyclopentyl group (x=5, y=9), perfluorocyclohexylgroup (x=6, y=11), and perfluoro(1-cyclohexyl)methyl group (x=7, y=13).

The aryl groups in which the hydrogen atom has been substituted by thefluorine atom can be exemplified by the pentafluorophenyl group (x=6,y=5) and 3-trifluoromethyltetrafluorophenyl group (x=7, y=7).

Among C_(x)F_(y) groups with formula (1), the linear alkyl groups,branched-chain alkyl groups, and aryl groups are preferred from thestandpoint of the ease of acquisition and the decomposability of thesulfonate ester moiety. The linear alkyl groups and aryl groups are morepreferred. The trifluoromethyl group (x=1, y=3), pentafluoroethyl group(x=2, y=5), heptafluoro-n-propyl group (x=3, y=7), nonafluoro-n-butylgroup (x=4, y=9), and pentafluorophenyl group (x=6, y=5) areparticularly preferred.

From the standpoint of the fixing performance, the compound with formula(1) is more preferably a compound represented by the following formula(2).

[In formula (2), x represents an integer of at least 1 and not more than8 and y represents an integer of at least 3 and not more than 17. R₃ andR₄ each independently represent an alkyl group, alkyloxy group,alkylthio group, aryl group, aryloxy group, or arylthio group, and o andp represent integers of at least 0 and not more than 3. When o is equalto or greater than 2, a plurality of the R₃ may be bonded to each otherto form a ring structure, and when p is equal to or greater than 2, aplurality of the R₄ may be bonded to each other to form a ringstructure. In addition, an R₃ and R₄ may be bonded to each other to forma ring structure.]

Preferably R₃ and R₄ each independently represent an alkyl group havingat least 1 and not more than 18 carbons, an alkyloxy group having atleast 1 and not more than 18 carbons, an alkylthio group having at least1 and not more than 18 carbons, an aryl group having at least 1 and notmore than 14 carbons, an aryloxy group having at least 1 and not morethan 14 carbons, or an arylthio group having at least 1 and not morethan 14 carbons.

Specific examples (exemplary compounds A-1 to A-27) of the cationicpolymerization initiator represented by formula (1) are provided below,but the present invention is not limited to these examples.

A single cationic polymerization initiator or a combination of two ormore can be used. In addition, a cationic polymerization initiator otherthan a compound with formula (1) may be incorporated to the extent thatthe effects of the present invention are not impaired.

The content of the cationic polymerization initiator is preferably atleast 0.01 mass part and not more than 10 mass parts per 100 mass partsof the curable insulating liquid.

<Curable Insulating Liquid>

Curable insulating liquids usable in the present invention are liquidsthat are made of cationically polymerizable monomer, have a high volumeresistivity, are electrically insulating, and have a low viscosity ataround room temperature, but are not otherwise particularly limited.

The cationically polymerizable monomer can be exemplified by vinyl ethercompounds, epoxy compounds, acrylic compounds, and oxetane compounds.

Among these, vinyl ether compounds are preferred from the standpoint ofhuman safety, high resistance, and low viscosity.

Here, vinyl ether compound refers to a compound that has a vinyl etherstructure (—CH═CH—O—C—).

This vinyl ether structure is preferably represented by R—CH═CH—O—C— (Ris hydrogen or C₁₋₃ alkyl and is preferably hydrogen or methyl).

The vinyl ether compound can be exemplified by butylethylpropanedioldivinyl ether (BEPDVE), n-octyl vinyl ether, 2-ethylhexyl vinyl ether,dodecyl vinyl ether, octadecyl vinyl ether, benzyl vinyl ether,dicyclopentadiene vinyl ether, cyclohexanedimethanol divinyl ether,tricyclodecane vinyl ether, trimethylolpropane trivinyl ether,2-ethyl-1,3-hexanediol divinyl ether, 2,4-diethyl-1,5-pentanedioldivinyl ether, 2-butyl-2-ethyl-1,3-propanediol divinyl ether, neopentylglycol divinyl ether, pentaerythritol tetravinyl ether, and1,2-decanediol divinyl ether.

A photopolymerization initiator and/or a photopolymerization sensitizermay also be used in combination with the cationically polymerizablemonomer. Any known compound can be used for this photopolymerizationinitiator or photopolymerization sensitizer as long as it does notexcessively lower the volume resistivity of the liquid developer anddoes not excessively increase its viscosity.

<Binder Resin>

A known binder resin that exhibits a fixing performance for theadherend, e.g., paper or plastic film, can be used as the binder resinas long as it is insoluble in the curable insulating liquid. Here,“insoluble in the curable insulating liquid” indicates that not morethan 1 mass part of the binder resin dissolves in 100 mass parts of thecurable insulating liquid.

Such a binder resin can be exemplified by epoxy resins, polyesterresins, (meth)acrylic resins, styrene-(meth)acrylic resins, alkydresins, polyethylene resins, ethylene-(meth)acrylic resins, androsin-modified resins. As necessary, a single one of these may be usedor two or more may be used in combination.

The content of the binder resin is not particularly limited, but ispreferably at least 50 mass parts and not more than 1,000 mass parts per100 mass parts of the carbon black.

The toner particle concentration in the liquid developer is preferablyat least 1 mass % and not more than 70 mass %.

The present inventors also discovered that—when the toner particlecontains a carbon black dispersing agent and this carbon blackdispersing agent has a dispersing group and an adsorptive group, and theadsorptive group is an amino group—the dark polymerization reaction canbe inhibited while also obtaining an excellent fixing performance.

As noted above, the dark polymerization reaction is produced by theaction of acidic functional groups on the carbon black surface on thephotopolymerization initiator present in the liquid developer.

Focusing on this reaction mechanism, the present inventors then foundthat an inhibitory effect on the dark polymerization reaction isobtained by the bonding of the acidic functional groups resident on thecarbon black surface with the amino group present in the adsorptivegroup of the carbon black dispersing agent.

The details of usable carbon black dispersing agents are provided in thefollowing.

<Carbon Black Dispersing Agent>

The carbon black dispersing agent characteristically has a dispersinggroup and an adsorptive group wherein the adsorptive group is an aminogroup.

The dispersing group can be, e.g., a hydrophobic group, for example, along-chain (preferably about 8 to 100 carbons) alkyl group.

This carbon black dispersing agent can be exemplified by Ajisper PB821and Ajisper PB881 from Ajinomoto Fine-Techno Co., Inc. and Solsperse11200 and Solsperse 18000 from Lubrizol Japan Limited. A single carbonblack dispersing agent or a combination of two or more can be used.

From the standpoint of the dispersibility, the content of the carbonblack dispersing agent is preferably at least 1 mass part and not morethan 100 mass parts per 100 mass parts of the carbon black.

There is no particular limitation on the method for adding the carbonblack dispersing agent, but from the standpoint of the dispersibility itis preferably mixed with and dispersed into the carbon black prior tomixing the carbon black with the binder resin.

<Toner Particle Dispersing Agent>

A toner particle dispersing agent may also be used in the liquiddeveloper. The toner particle dispersing agent functions to stablydisperse the toner particles in the curable insulating liquid, and thereare no particular limitations on the type as long as it can be used forthis purpose. The toner particle dispersing agent may undergodissolution or dispersion in the carrier liquid. Examples of suchdispersing agents are Ajisper PB817 from Ajinomoto Fine-Techno Co., Inc.and Solsperse 11200, 13940, 17000, and 18000 from Lubrizol JapanLimited. This dispersing agent may be added at at least 0.5 mass partsand not more than 30 mass parts per 100 mass parts of the tonerparticle. The toner particle dispersibility is further improved by usewithin this range.

<Charge Adjuvant>

A charge adjuvant can be incorporated with the goal of adjusting thecharging behavior of the toner particle. A known charge adjuvant can beused.

Examples of specific compounds are as follows: metal soaps such aszirconium naphthenate, cobalt naphthenate, nickel naphthenate, ironnaphthenate, zinc naphthenate, cobalt octanoate, nickel octanoate, zincoctanoate, cobalt dodecanoate, nickel dodecanoate, zinc dodecanoate,aluminum stearate, aluminum tristearate, and cobalt 2-ethylhexanoate;metal sulfonates such as petroleum-based metal sulfonates and the metalsalts of sulfosuccinate esters; phospholipids such as lecithin; metalsalicylates such as metal t-butylsalicylate complexes;polyvinylpyrrolidone resins; polyamide resins; sulfonic acid-containingresins; and hydroxybenzoic acid derivatives.

<Other Substances>

Various known additives may as necessary be used in the liquid developerof the present invention with the goal of improving the compatibilitywith recording media, the image storability, and other characteristics.For example, surfactant, lubricant, filler, antifoaming agent,ultraviolet absorber, antioxidant, anti-fading agent, anticorrosionagent, and so forth can be selected and used as appropriate.

<Production Method>

The method of producing the liquid developer is not particularly limitedin the present invention and can be exemplified by known methods, forexample, the coacervation method and the wet pulverization method.

The details of the coacervation method are described in, for example,Japanese Patent Application Laid-open No. 2003-241439, WO 2007/000974,and WO 2007/000975.

In the coacervation method, carbon black, binder resin, solvent thatdissolves the binder resin, and solvent that does not dissolve thebinder resin are mixed and the solvent that dissolves the binder resinis then removed from the mixture to cause the binder resin that had beendissolved to precipitate, thereby creating a dispersion of carbonblack-enclosing toner particles in the solvent that does not dissolvethe binder resin.

The details of the wet pulverization method, on the other hand, aredescribed in, for example, WO 2006/126566 and WO 2007/108485.

In the wet pulverization method, the carbon black and binder resin arekneaded at or above the melting point of the binder resin; this isfollowed by a dry pulverization; and the obtained pulverized material issubjected to a wet pulverization in an electrically insulating medium,thereby dispersing the toner particles in the electrically insulatingmedium.

Known methods such as these can be used in the present invention.

The methods used to measure the properties related to the presentinvention are described in the following.

(1) pH of the Carbon Black

The pH of the carbon black was measured based on JIS K 6221-1982.

(Separation of the Carbon Black in the Liquid Developer)

The carbon black is separated from the liquid developer by the followingmethod to enable measurement of the pH and specific surface area. Thecarbon black in the toner can be extracted by subjecting the toner to adispersion treatment in toluene to dissolve the binder resin and by thenseparating the carbon black using filter paper and subjecting it to awashing and drying process.

(2) Measurement of the Substituents on the Carbon Black Surface

The substituents on the carbon black surface were measured by carryingout analysis of the surface composition using X-ray photoelectronspectroscopy (instrument name: PHI 5000 VersaProbe II, ULVAC-PHI, Inc.).

The principal conditions are as follows.

output: 100μ, 25 W, 15 kVmeasurement range: 300 μm×300 μm

Pass Energy: 23.5 eV Step Size: 0.1 eV

The surface substituent groups on the carbon black were identified inthe present invention using the peak intensities measured for theindividual elements and the relative sensitivity factors provided byULVAC-PHI, Inc.

(3) Measurement of the Specific Surface Area (BET) of the Carbon Black

The BET specific surface area of the carbon black was measured based onJIS Z 8830 (2001). The specific measurement method is as follows.

A “TriStar 3000 Automatic Specific Surface Area Porosimetry Analyzer”(Shimadzu Corporation), which uses gas adsorption by a constant volumeprocedure as its measurement methodology, was used as the measurementinstrument. The measurement conditions were set and the measurement datawas analyzed using “TriStar 3000 Version 4.00”, the dedicated softwareprovided with this instrument. A vacuum pump, nitrogen gas line, andhelium gas line were connected to the instrument. The value calculatedusing a multipoint BET method and using nitrogen gas as the adsorptiongas was used as the specific surface area of the carbon black in thepresent invention.

(4) Compositional Analysis

The following procedure was used for the structural identification ofthe compounds and so forth.

Measurement of the ¹H-NMR and ¹³C-NMR spectra was carried out using anECA-400 (400 MHz) from JEOL Ltd.

The measurements were carried out at 25° C. in a deuterated solventcontaining tetramethylsilane as the internal reference substance. Thechemical shift value was reported as the shift value in ppm (6 value)using 0 for the tetramethylsilane internal reference substance.

EXAMPLES

The basic constitution and characteristics of the present invention aredescribed above, while the present invention is specifically describedin the following based on examples. However, the present invention is inno way limited to or by these.

Unless specifically indicated otherwise, the parts and % in thefollowing blends indicate, respectively, mass parts and mass %.

<Carbon Black 1>

Carbon black 1 having a BET of 65 m²/g was obtained by introducing NaOHinto the furnace using an alkali burner during carbon black productionby the furnace method.

When the resulting carbon black 1 was analyzed, Na originating fromCOONa groups that were functional groups residing on the carbon blacksurface was detected. The pH was 9.0.

<Carbon Black 2>

Carbon black 2 was obtained proceeding as in the production example forcarbon black 1, but changing the NaOH to KOH. The property values forcarbon black 2 are given in Table 1.

<Carbon Black 3>

#4000B (Mitsubishi Chemical Corporation) was used as carbon black 3. Theproperty values for carbon black 3 are given in Table 1.

<Carbon Black 4>

Printex L (Orion Engineered Carbons) was used as carbon black 4. Theproperty values for carbon black 4 are given in Table 1.

<Carbon Black 5>

Printex 85 (Orion Engineered Carbons) was used as carbon black 5. Theproperty values for carbon black 5 are given in Table 1.

<Carbon Black 6>

Printex 95 (Orion Engineered Carbons) was used as carbon black 6. Theproperty values for carbon black 6 are given in Table 1.

<Carbon Black 7>

Color Black FW18 (Orion Engineered Carbons) was used as carbon black 7.The property values for carbon black 7 are given in Table 1.

<Carbon Black 8>

MA77 (Mitsubishi Chemical Corporation) was used as carbon black 8. Theproperty values for carbon black 8 are given in Table 1.

<Carbon Black Dispersing Agents 1 to 3>

The carbon black dispersing agents 1 to 3 used in these examples andcomparative examples are given in Table 2.

<Binder Resin>

bisphenol A/2.3 mol ethylene 40 parts oxide adduct (BPA-EO) terephthalicacid (TFA) 40 parts tetrabutyl titanate (TNBT) 0.2 parts 

These materials were introduced and a reaction was carried out for 10hours under a nitrogen current at 220° C. while distilling out theproduced water. A reaction was then carried out under a reduced pressureof 5 to 20 mmHg, followed by cooling to 180° C. and the addition of 20parts of trimellitic anhydride (TMA). A reaction was carried out for 2hours at normal pressure under seal, and this was followed by removal,cooling to room temperature, and then pulverization to obtain apolyester resin. The resulting polyester resin was dissolved in THF at50 mass % to provide the binder resin used in the present invention.

<Liquid Developer 1>

carbon black 1: 10 parts carbon black dispersing agent: 10 parts(Ajisper PB-821, contains amino group, Ajinomoto Fine-Techno Co., Inc.)tetrahydrofuran (THF): 80 partswere mixed and were stirred for 1 hour with a paint shaker using glassbeads having a diameter of 2 mm to obtain a pigment-dispersed slurry 1.Then,

pigment-dispersed slurry 1: 60 parts binder resin (the previouslydescribed solution 80 parts of resin dissolved in THF at 50 mass %):toner particle dispersing agent: 12 parts (Ajisper PB-817, basic,Ajinomoto Fine-Techno Co., Ltd.)were mixed with a high-speed disperser (T.K. Robomix/T.K. HomodisperModel 2.5 blade, Primix Corporation) and mixing was carried out whilestirring at 40° C. to obtain a pigment dispersion 1.

While stirring at high speed (rotation rate=15,000 rpm) using ahomogenizer (Ultra-Turrax T50, IKA-Werke GmbH & Co. KG), 200 parts ofdodecyl vinyl ether (DDVE) was added in small portions to the pigmentdispersion 1 (100 parts) obtained as described above to obtain a mixture1.

The obtained mixture 1 was transferred to a pear-shaped recovery flaskand the THF was completely distillatively removed at 50° C. whileperforming ultrasound dispersion, to obtain a toner particle dispersion1 containing toner particles in a curable insulating liquid.

The resulting toner particle dispersion 1 (10 parts) was subjected to acentrifugal separation process; the supernatant was removed bydecantation; replacement was carried out with fresh DDVE in the sameamount as the removed supernatant; and redispersion was performed.

A liquid developer 1 was then obtained by the addition of 0.10 parts ofa hydrogenated lecithin (product name: Lecinol S-10, Nikko ChemicalsCo., Ltd.), 90 parts of butylethylpropanediol divinyl ether (BEPDVE) asthe curable insulating liquid (liquid polymerizable monomer), 0.30 partsof a cationic polymerization initiator (product name: NHNI-PFBS, ToyoGosei Co., Ltd.), and 1 parts of KAYAKURE-DETX-S (Nippon Kayaku Co.,Ltd.).

The toner particles present in the resulting toner particle dispersionhad a volume median diameter D50 of 0.7 μm.

(The toner particle size distribution was measured using a Nanotrac 150(Nikkiso Co., Ltd.), which is a particle size distribution analyzerbased on dynamic light scattering (DLS)).

<Liquid Developers 2 to 14>

Liquid developers 2 to 14 were obtained proceeding as in the productionof liquid developer 1, but changing the carbon black, curable insulatingliquid, cationic polymerization initiator, and carbon black dispersingagent as shown in Table 3. The composition and properties of liquiddevelopers 2 to 14 are given in Table 3.

Example 1 (Dark Polymerization Reaction)

The liquid developer 1 was held in a dark location in a 50° C.environment and the occurrence of curing due to the dark polymerizationreaction was checked on each day of standing. The following criteriawere then used for the evaluation.

AA: No curing after at least 30 days.

A: Cured at day 21 to 30. B: Cured at day 16 to 20. C: Cured at day 11to 15. D: Cured at day 6 to 10.

E: Cured within 5 days.

(Fixing Performance)

The liquid developer was dripped onto a polyethylene terephthalate filmat room temperature (25° C.) in an environment with a 50% humidity; barcoating (the thickness of the resulting film was 13.7 μm) was performedusing a wire bar (No. 6) [supplier: Matsuo Sangyo Co., Ltd.]; and acured film was formed by exposure to an LED having an emissionwavelength of 385 nm (illuminance: 1,000 mW/cm², exposure distance: 15mm). The exposure dosage when surface tack (stickiness) was absent andcuring was completed was measured and was evaluated using the followingcriteria.

A: at least 100 mJ/cm² and less than 500 mJ/cm²B: at least 500 mJ/cm² and less than 1,000 mJ/cm²C: at least 1,000 mJ/cm² and less than 2,000 mJ/cm²D: at least 2,000 mJ/cm² or curing did not occur

The results of the evaluations in Example 1 are given in Table 4.

Examples 2 to 12

Evaluations were carried out in Examples 2 to 12 proceeding as inExample 1, but changing the liquid developer from that in Example 1. Theresults of the evaluations are given in Table 4.

Comparative Examples 1 and 2

Evaluations were carried out in Comparative Examples 1 and 2 proceedingas in Example 1, but changing the liquid developer from that inExample 1. The results of the evaluations are given in Table 4.

TABLE 1 BET alkali metal-substituted carbon black No. pH (m²/g)functional group 1 9.0 65 Na 2 10.0 80 K 3 10.0 100 none 4 9.0 150 none5 9.5 200 none 6 9.5 250 none 7 4.5 260 none 8 2.5 130 none

TABLE 2 carbon black presence/ dispersing absence of agent No. productname manufacturer amino group 1 Ajisper PB821 Ajinomoto Fine-Technopresent Co., Ltd. 2 Ajisper PB881 Ajinomoto Fine-Techno present Co.,Ltd. 3 Solsperse 36000 Lubrizol Japan Limited absent

TABLE 3 materials cationic carbon black toner particle liquidpolymerization dispersing agent diameter D50 developer No. carbon blackNo. initiator curable insulating liquid No. (μm) 1 1 A-26 BEPDVE 1 0.7 21 A-23 trimethylolpropane 1 0.8 trivinyl ether 3 1 A-26 BEPDVE 1 0.7 4 2A-26 BEPDVE 1 0.7 5 1 A-26 BEPDVE 2 0.7 6 1 A-8  BEPDVE 1 0.7 7 3 A-8 BEPDVE 1 0.9 8 4 A-8  BEPDVE 1 0.9 9 5 A-8  BEPDVE 1 0.5 10 6 A-8 BEPDVE 1 0.7 11 7 A-8  BEPDVE 1 0.7 12 6 A-8  BEPDVE 3 0.7 13 8 A-26BEPDVE 3 0.7 14 8 A-26 BEPDVE none 0.7

TABLE 4 liquid dark fixing developer No. polymerization performanceExample No. 1 1 AA A 2 2 AA A 3 3 AA A 4 4 AA A 5 5 AA A 6 6 AA B 7 7 AAB 8 8 A B 9 9 B B 10  10 C B 11  11 D C 12  12 D C Comparative ExampleNo. 1 13 E D 2 14 E D

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2016-156444, filed Aug. 9, 2016, and Japanese Patent Application No.2017-140110, filed Jul. 19, 2017, which are hereby incorporated byreference herein in their entirety.

What is claimed is:
 1. A liquid developer comprising a curableinsulating liquid, a cationic polymerization initiator, and a tonerparticle containing a binder resin and carbon black, wherein the carbonblack is basic.
 2. The liquid developer according to claim 1, whereinthe carbon black has a functional group obtained by substitution, by analkali metal, of a hydrogen atom in an acidic group that is a surfacefunctional group.
 3. A liquid developer comprising a curable insulatingliquid, a cationic polymerization initiator, and a toner particlecontaining a binder resin and carbon black, wherein the toner particlecontains a carbon black dispersing agent, and the carbon blackdispersing agent has a dispersing group and an adsorptive group, and theadsorptive group is an amino group.
 4. The liquid developer according toclaim 1, wherein the specific surface area (BET) of the carbon black isnot more than 200 m²/g.
 5. The liquid developer according to claim 1,wherein the cationic polymerization initiator contains a compoundrepresented by the following formula (1);

where, in formula (1), R₁ and R₂ are bonded to each other to form acyclic structure; x represents an integer of at least 1 and not morethan 8; and y represents an integer of at least 3 and not more than 17.6. The liquid developer according to claim 3, wherein the specificsurface area (BET) of the carbon black is not more than 200 m²/g.
 7. Theliquid developer according to claim 3, wherein the cationicpolymerization initiator contains a compound represented by thefollowing formula (1);

where, in formula (1), R₁ and R₂ are bonded to each other to form acyclic structure; x represents an integer of at least 1 and not morethan 8; and y represents an integer of at least 3 and not more than 17.